A known technique of providing local time information to selective call radios, such as pagers, that are used in wide area simulcast communication systems is to periodically include a local time in a signaling protocol transmitted from a plurality of transmitters. The well known FLEX.TM. signaling protocol is an example of such a signaling protocol. In a typical metropolitan simulcast communication system, all the coverage area is within one time zone. The local time is accurately determined, for example, from a Global Positioning System satellite, and used in the protocol of the radio signals transmitted by all the transmitters in the system. For example, the local time periodically transmitted in a FLEX.TM. signaling protocol from all the transmitters in a communication system covering the Los Angeles area would be made current with reference to the time for the Pacific Time Zone. However, in a simulcast communication system that has coverage in more than one time zone, a problem exists in that the local time transmitted is not correct in all portions of coverage of the system. This is illustrated in FIG. 1, which is an idealized coverage map showing coverage of a portion of a plurality of radio transmitters used in a prior art simulcast radio communication system 100 near a time zone border 120. The time zone border 120 in this example is the border between the Central Time Zone (CTZ) and Eastern Time Zone (ETZ) in the United States. Coverage areas (or cells) 111-119 of ten transmitters are illustrated with circular boundaries, which are idealized representations of real boundaries at which the reliability of receiving a message falls below a predetermined limit. The simulcast radio communication system 100 further comprises selective call radios (SCRs), of which six SCRs 131-136 are shown in FIG. 1. It will be appreciated that the concepts described herein using the idealized representations are equally valid for real cells having boundaries that are non-circular. Because the radio communication system 100 is a simulcast system, the six SCRs 131-136 shown in FIG. 1 are all adjusted to receive at a common frequency. The local time for the ETZ is transmitted periodically, for example every four minutes, by all transmitters in the simulcast radio communication system 100, including the transmitters for cells 111-119 shown in FIG. 1. This is indicated by the use of horizontal cross hatch lines in FIG. 1. ETZ time was chosen because a preponderance of the geographic coverage of the simulcast radio communication system 100 is in the ETZ. SCRs 132, 134, 136 are located in overlap regions between two cells, indicated by the denser horizontal cross hatch lines. In a well adjusted simulcast system, SCRs in the overlap regions will receive signal with approximately the same reliability as SCRs located in non-overlap regions. SCRs 131-134 are located in the CTZ, and SCRs 135, 136 are located in the ETZ. Accordingly, SCRs 131-134 receive a wrong local time, while SCRs 135, 136 will typically receive the correct local time.
In accordance with one variation of the prior art simulcast radio communication system 100 described above, an additional bit is used in the protocol transmitted by all the transmitters of the simulcast radio communication system 100 that identifies the system as extending over at least one time zone boundary, thereby alerting a user that the time received may not be accurate. Users who use the system regularly and are aware of which time zone they are in can therefore deduce the correct time. However, users who use the system infrequently, and particularly visiting users (roaming users), are likely to be confused about the correct time local time, although they can be alerted to the situation.
Thus, what is needed is a method for improving the presentation of local time information in a simulcast radio communication system.